Air testing device



Mardl 1941. R. w. MOALLISTER 34, 9

AIR TESTING DEVICE Original Filed April 27, 1937 2 Sheets-Sheet 1 "'I' (flfllllllllll sI /IIIIIIIIIIIIIIIIIII 7'2: ATTORNEYS.

March 11, 1941. R w MOALLISTER 2,234,499

AIR TESTING DEVICE Original Filed April 27, 1937 2 Sheets-Sheet 2 INVENTOR. M 3344465. @614, 64x44 26;

M ATTORNEYS.

Patented Mar. 11, 1941 UNITED STATES ATENT OFFICE AIR TESTING DEVICE Robert W. McAllister, Carlisle, Mass., Mine Safety Appliances Company,

assignor to Pittsburgh,

Pa., a corporation of Pennsylvania Claims.

The present invention relates to the detection of gases in gas mixtures; more particularly, it relates to an apparatus for detecting and determining the concentration of toxic gases, e. g., hydrocyanic acid gas, in air mixtures.

Various means of detecting the presence of gases such as hydrocyanic acid gas in air mixtures have been previously proposed. These means, which generally require the use of liquid test solutions or test papers, are not entirely satisfactory for general application outside the laboratory. The use of test solutions is inconvenient and requires considerable experience in order to obtain reasonably accurate results, while the use of test paper is not always reliable, especially when quantitative determinations are required.

There is a very definite need of a reliable, simple apparatus for determining whether or not toxic concentrations of hydrocyanic acid gas are present in atmospheres of previously fumigated. Although the general practice is to ventilate premises thoroughly after fumigation, there is always the possibility that spaces which are not easily ventilated. Furthermore, even though a room which has been fumigated with hydrocyanic acid gas is subsequently ventilated, toxic concentrations of the gas frequently remain near substances which absorb the gas. Thus, in the fumigation of grains, thorough aeration of the material to remove hydrocyanic acid gas is difficult and there always remains the possibility that human beings may enter spaces enclosing the grains before the hydrocyanic acid gas has been completely removed. Hydrocyanic acid gas has been known to be present in grain storage rooms weeks after fumigation has been completed. As far as I am aware, there never has been developed a successful apparatus for rapidly and reasonably accurately determining the concentration of hydrocyanic acid gas in air mixtures, so that the presence or absence of toxic concentrations may be ascertained in a convenient, practical manner.

A major object of the invention is to provide a compact, simple apparatus which is especially well suited for rapidly determining concentrations of gases, e. g., hydrocyanic acid gas in mixture with air, and which is convenient and reliable in use. Other objects will be hereinafter apparent.

The invention will be described with reference to the accompanying drawings which represent a desirable embodiment and in which Fig. 1' is a side elevational view of the apparatus;

spaces which have been toxic concentrations of the gas may remain in Fig. 2 a longitudinal sectional view taken on line 11-11 of Fig. 4; Fig. 3 a sectional view on line III-III of Fig, 1, shown partially in elevation with trigger and ratchet pawl omitted; and Figs. 4 and 5 rear and front elevational views, respectively, with the aspirator bulb not shown.

Having reference now to the drawings, the embodiment shown comprises a body, or frame, member 10 through which a bolt ll extends longitudinally to serve as a removable shaft around 1 which a magazine l2 may be rotated within body It. Magazine l2 includes rear and front circular end plates I3 and M, respectively, which are provided with apertures I5-tapered from the inside to receive the rubber sleeve extensions [6 of the glass detector tubes or cartridges H. The rubber sleeve extensions l6 protect the ends of the detector tubes 11, permit their removal from the magazine, and insure a gas-tight fit of the tubes against the sides of the apertures l5. Apertures 15 are so made that upon rotation of the magazine [2, adjacent pairs of apertures on end plates l3 and M are successively aligned with a pair of aligned rubber washers l8 situated one at the rear end of the body l0 and the other at the inner end of an inlet tube l9 mounted in the forward end of the body, as shown in Fig. 2. When any pair of said apertures is so aligned, orifice 20 in the rear end of body l0 permits the aspiration of gas from inlet tube l9 through the detector tube positioned between the aligned pair of apertures, upon manipulation of the aspirator bulb 2| connected to orifice 20. Bulb 2| is provided with a valve 22 which functions to regulate the flow of gas tube in one direction only, from front to back, upon manipulation of the aspirator bulb 2|. Inlet tube I9 also serves as an adjustment means by which the end plates l3 and M of magazine l2 are maintained tightly against rubber washers It so as to form a continuous gas-tight passage for the gas mixture from the inlet tube through the aligned detector tube into bulb 2|, and to this endtube I9 is threaded through frame l0 so that any degree of tension of end plates [3 and M against washers l8 may be maintained.

Trigger 23, together with ratchet wheel 24 and ratchet pawl 25, provides a means for rotating magazine l2. Trigger stop 26 functions to arrest the rotation caused by each pull of the trigger when each successive detector tube is brought into proper alignment with inlet tube l9 and orifice 20. Trigger spring 21 functions to return the trigger to its normal resting position after each pull thereof and pawl spring 28 serves through the detector 3 to maintain the ratchet pawl in operative contact with the teeth of ratchet wheel 24. Element 29 is a handle which may 'or may not be a part of the apparatus, since its use is more a matter of convenience rather than a necessity.

The apparatus illustrated by the drawings is simple to operate. The detector tubes I! are filled with an appropriate detector composition 3U, suitably a granular absorbent material impregnated with a reagent which changes color upon contact with the gas to be determined, as described more fully hereinafter. Composition 3D is held in position in the 3|. The filled tubes then are inserted into the magazine and the rubber sleeves adjusted so that the tubes are held snugly in position. Inlet tube l9 then is placed in the gas mixture to be tested and the aspirator bulb is squeezed the required number of times in order to draw through the detector tube the desired amount of the gas mixture. Thus, if a volume of 600 cc. is desired and the aspirator bulb has a capacity of 60 00., ten. squeezes will be necessary. The distance from the front of the detector composition in the detector tube which changes color is an indication of the concentration of the gas to be determined in the gas mixture being tested. By comparing the length of travel of coloration in the tube with a similar length of travel ob tained using corresponding detector tubes and gas v mixtures containing known concentrations of the gas to be determined, a quantitative measure of the concentration of the gas in the gas mixture is obtained.

After one determination as described above, the trigger is pulled to bring into proper alignment a second detector tube. The apparatus then is ready for use to make a second determination. The apparatus may be employed repeatedly until all of the detector tubes in the magazine have been used.. The magazine then may be refilled with new detector tubes or the old tubes may be removed and refilled for further use. Although. not illustrated in the drawings,.the detector tubes may be calibrated so that concentrations may be read directly in per cent or parts per million. may be provided with a calibratedscale positioned in close proximity to the detector tube in use, from which the concentration may be read directly in any desired unit.

The purpose of orifice 20 is to prevent anysubstantial back flow of spent gas through the detector tube upon squeezing bulb 2|, and also to prevent gas from being drawn too rapidly through thedetector tube when the bulb is permitted to assume its original shape after being squeezed. In order for accurate results to be obtained,.the gas should be passed through the detector tubes at a rate no faster than the maximum rate at which the gas to be determined is completely adsorbed by the composition in the tubes. The size of orifice that .should be employed canbe readily, determined by a few tests.

I have illustratedan apparatus which contains eight detector tubes or cartridges in the magazine. -It is to be understood that the :magazine and apparatus may be so constructed as to contain a greater or lesser number of cartridges without: departing-fromthe spirit of my invention; Other modifications may likewise be made. Thus, instead of using a bulb and handle as illustrated in the drawings, the handle may beomitted entirely, or a rubber handle which serves tubes by cotton plugs If desired, the apparatus both as an aspirator and as a handle may be used with good results.

My invention is not to be restricted by the drawings, examples, or procedural details herein set forth, which are intended to be illustrative and not restrictive in nature.

Although various types of color change reagents may be used in the practice of this invention, those disclosed in my copending application Serial No. 139,332, filed April 27, 1937, of which this application is a division, now Patent No. 2,l76,462, granted October 17, 1939, are particularly suitable. Such reagents comprise granular adsorptive material coated or impregnated with a reagent which changes color upon contact with the constituent to be determined in a gas mixture.

Likewise, the present invention affords a satisfactory means for practicing the method disclosed in the aforesaid parent application. That tion in the mixture is to be determined, through a column of a granular adsorptive material coated or impregnated with a color-forming agent which is sensitive to the gas constituent being determined. The length of travel of coloration in the column of granular adsorptive material is proportional to the concentration of the gas being determined in the gas mixture, provided the cross-section of the column is uniform throughout its length. By observing the length of travel of the coloration through the column and comparing it with the corresponding length of travel in a similar column employed using a gas mixture having a known concentration of the gas being determined, it is possible to measure quantitatively the concentration of the gas in the mixture being tested. Such method may be practiced using various types of equipment, but the apparatus disclosed and claimed herein is especially well suited for practicing the method.

The term color-forming agent is used in the ensuing description and in the appended claims to mean a substance or composition which develops a distinct .color, or undergoes a distinct color change, when contacted with the gas whose concentration in a gas mixture is being determined. The term granular adsorptive materia1 is used to designate a granular material which is a good adsorbent for the gas whose concentration is being determined.

Various chemical compounds are known to become colored, or to undergo a distinct color change, when they are contacted with certain gases. Thus, o-tolidine is sensitive in this manner to chlorine; p-amino dimethyl amidine'hydrochloride to hydrogen sulfide; thiocyanate to iron carbonyl; p-rosaniline hydrochloride to formaldehyde; and benzidine acetate and numerous other substances are sensitive to hydrocyanic acid. I have discovered that such colorformingsubstances may be employed effectively to determine quantitatively various toxic gases in gasmixtures if they are uniformly coated over, or impregnatedinto, granular adsorptive materials instead of being used in the form of solution or on test papers as they have been employed heretofore.

The column of granular material which is coated or impregnated with the color-forming substance may be conveniently prepared by packing the material in a glass tube having a suitable diameter. In order for the results to be reasonably accurate, it is essential that the tubes employed have a substantially uniform diameter form size and not too large. On the other hand,

the granules should not be so small as to increase appreciably the resistance of the column to the flow of gas therethrough. Particles having a size corresponding to 20 to 40 mesh may be used in most instances with good results, although I have found that it is generally preferable to employ particles having a size within the range of 30 to 34 mesh. For ordinary use, tubing having an inside diameter of 6 to 9 millimeters is generally satisfactory, although smaller or larger size tubing may be employed depending upon the concentration of the gas being determined in the gas mixtures.

It is essential that the color-forming agent be stable in contact with the granular material upon which it is coated. It is also essential that the agent be not sensitive to more than one constituent of the gas mixture. I have found that for most determinations that are required in connection with fumigation with hydrocyanic acid gas, the use of a composition containing benzidine acetate and cupric acetate as the color-forming substance is very satisfactory. Similarly, for the determination of chlorine, o-tolidine is especially suitable, while p-rosaniline hydrochloride may be used with good results for the determination of formaldehyde vapors in gas mixtures. Other color-forming agents may be employed, in accordance with my invention, for the determination of the above gases, and it is to be understood that the illustrations herein set forth are merely illustrative of my invention.

A suitable method for preparing the detector mixture, i. e., the granular material impregnated with the color-forming agent, for use in the determination of hydrocyanic acid gas is as follows:

A saturated solution of benzidine acetate in methyl alcohol is prepared, as well as a second solution containing 14 grams of cupric acetate in 200 cc. of water. Each of the above solutions are filtered to remove insoluble materials therefrom. 50 cc. portions of each solution then are added to 100 cc. of methyl alcohol and the resulting mixture diluted with 500 cc. of water. After standing for about fifteen minutes, the solution is filtered to remove the dark precipitate that is formed, whereby a clear, greenish colored solution is generally obtained. If a clear solution is not obtained, filtration should be repeated. The clear solution then is poured over 30 grams of the granular adsorptive material, e. g. alumina gel, contained in a small Buchner funnel fitted with a filter paper and the liquid drawn off at once. The treated granular material is then placed upon paper to dry. Drying is continued until the material is just wet enough to be picked up upon contact with the finger tips without extra pressure from the hand. The treated granular material then is placed in stoppered, air-tight containers for storage until required for use.

Alumina gel of 30 to 34 mesh was treated in the above manner and then packed into 3-inch lengths of 6 millimeter glass tubing so as to form several compartments of uniform length in each tube, the individual compartments being separated from each other by plugs of absorbent cotton. The following table illustrates the accuracy with which hydrocyanic acid gas may be determined in air in accordance with my invention:

Number of compartments penetrated by the coloration Percent by 110mm;

Repeated laboratory tests have shown that check results may be obtained withgas mixtures containing known concentrations of hydrocyanic acid and that the length of travel of coloration in a tube of a given cross section is proportional to the concentration of hydrocyanic acid in the gas mixture when equal volumes of gas are used in the determinations. It is not essential that the material be divided into compartments; equally satisfactory results have been obtained using a continuous column of the granular material impregnated with the color-forming agent.

Such reagent tubes may be employed to determinehydrocyanic acid over a wide range of concentrations. Thus, I have found that the method described is applicable to determine con-- centrations ranging from 1 part per million to 1 part per hundred by volume with a satisfactory degree of accuracy. The determinations are rapid and reliable since the color formed is a bright blue and can be easily detected even by inexperienced operators. Results which are accurate Within 10 per cent and. generally within per cent are readily obtainable.

Such detector tubes are applicable also in the determination of other gases, it being only necessary to employ a granular adsorptive material which is coated or impregnated with an agent that forms a distinct color or color change when contacted with the gas Whose concentration is to be determined. Thus, the granular adsorbent may be impregnated with an aqueous solution of o-tolidine for determining chlorine, which converts the colorless granules to an intense yellow or orange color. Or, the impregnant may be an aqueous solution of p-rosariiline hydrochloride (suitably decolorized with sodium bisulfide) for determining formaldehyde. And instead of the hydrocyanic acid reagent described above there may be used aloin or a methyl red-meruric,

to employ a color-forming material that is colorless, or substantially colorless, prior to its contact with the gas, in order that any color that is developed may be readily detected. It is also desirable that the color developed be relatively permanent although this is not an essential characteristic.

In the determination of hydrocyanic acid gas, chlorine, or formaldehyde vapors, it is essential that the porous impregnatedmaterial be moist when used; otherwise unreliable results may be obtained. I have found that alumina gel which has been impregnated with a benzidine acetatecupric acetate mixture is entirely satisfactory for determining hydrocyanic acid even after two months, provided it has been stored in a vaportight container. The material also may be used with good results even though the container in which it is stored is open to the atmosphere for several days before use. There may be some tendency for the mixture to assume a gray color; however, the intense blue oolorthat is developed in contact withhydrocyanic. acid is easilydetected even though the granular material has assumed such a gray color. The effectiveness of the material is not permanently destroyed by becoming dry, since by remoistening the dry material, its effectiveness is restored.

It is not always essential that the coated or impregnated granular material be used in a moistened condition. It is known that test papers for the dtermination of certain gas con' Various inert granular adsorbent materials may be used as a support for the color-forming agents. Examples'of such granular materials are alumina gel, silica gel, chipped ceramic Ware, shredded asbestos, and the like. It is preferable that the material be white in order not to obscure the color developed. It is essential that the granular supporting material be a good adsorbent for the gas which is to be determined.

The adsorbent acts to remove quantitatively the gas constituent from the gas mixture and thus -to bring it into intimate contact with the colorforming agent with which the adsorbent is impregnated. It is the eifectiveness of the adsorbent material in this respect which makes possible the obtainment of quantitative determinations by my method. Alumina gel is an excellent adsorptive supporting material for color-forming substances to be used in the determination of hydrocyanic acid since it is a good adsorbent for hydrocyanic acid gas. It is also excellent for use in the determination of chlorine or formaldehyde. Silica gel is almost as good as alumina gel although I prefer to use alumina gel.

According to the provisions of the patent statutes I have explained the principle and construction of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it under stood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and describech I claim 1. An apparatus forthe determination of a.

constituent of a gas mixture, the apparatus comprising, in combination, a body member, aspirating means associated with said member, and a magazine bearing a plurality of detector tubes containing reagent which changes color upon contact with the constituent to be determined, said magazine being rotatably associated with said body for presenting a detector tube to said aspirating means to pass gas mixture to be tested therethrough, and for bringing successive tubes into such relationship for successive tests.

2. An apparatus for the determination of a constituent of a'gas mixture,'the apparatus comprising, in combination, a body member, aspiratting means associated with said member, and a magazine bearing a plurality of detector tubescontaining reagent which changes color upon contact with the constituent to be determined;

said magazine being rotatably mounted in said body, and trigger-operated means for rotating said magazine to bring said tubes successively into gas communication relationship with a source ofgas mixture to be tested'and said aspirating means.

3. An apparatus for the determination of a constituent of a gas mixture, the apparatus comprising; in combination, a body member provided at its forward end with an inlet for gas'to be tested and at its rear end with a gas outlet passage, an aspirator bulb associated with said outlet passage; a magazine bearing a plurality of detector tubes containing granular adsorbent imsaid magazine being rotatablymounted in said body to bring said tubes into gas-communicating alignment with said gas inlet and outlet, and" -pregnated with an agent which changes color upa on contact with the constituent tobe determined, I

means for rotating said magazine to bring successive tubes into such alignment for successive tests.

4. Anapparatus according to claim 3, said inlet and outlet being provided with means cooperating with said tubes to prevent leakage while a CERTIFICATE OF CORRECTION. Patent No. 2,25L h99. March 11, 19LL1.

ROBERT w. McALLisTER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 9, for "absorbent" read -adsorbent-; page 5, second column, line 148, for "bisulfide" read -bisulfite-; line 51, for "red-meruric" read -red-mercuric-; and that the said Letters Patent should be read with this correction therein that the same may; conform to the record of the case in the Patent Office.

Signed and sealed'this 29th day of April, A. 11. 19b1.

Henry Van Arsdal-e, (Seal) Acting Commissioner of Patents. 

